Engineered plant biomass particles coated with bioactive agents

ABSTRACT

Plant biomass particles coated with a bioactive agent such as a fertilizer or pesticide, characterized by a length dimension (L) aligned substantially parallel to a grain direction and defining a substantially uniform distance along the grain, a width dimension (W) normal to L and aligned cross grain, and a height dimension (H) normal to W and L. In particular, the L×H dimensions define a pair of substantially parallel side surfaces characterized by substantially intact longitudinally arrayed fibers, the W×H dimensions define a pair of substantially parallel end surfaces characterized by crosscut fibers and end checking between fibers, and the L×W dimensions define a pair of substantially parallel top and bottom surfaces.

STATEMENT OF GOVERNMENT LICENSE RIGHTS

This invention was made with government support by the Small BusinessInnovation Research program of the U.S. Department of Energy, ContractSC0002291. The United States government has certain rights in theinvention.

FIELD OF THE INVENTION

Our invention relates to manufactured particles of plant biomass thatare coated with bioactive agents.

BACKGROUND OF THE INVENTION

As used herein, the term “bioactive agent” means a substance thataffects a living organism. Representative bioactive agents includeinorganic chemicals like fertilizer compounds, nutrients andmicronutrients; organic compounds like insecticides, herbicides andfungicides; and biochemical like enzymes, growth factors and oils. By“coating” is meant the uptake and reversible retention of a bioactiveagent onto or within the lignocellulosic matrix of a plant biomassmaterial.

It is well known in the art that biomass materials can serve as usefulcarriers for bioactive agents. Representative examples follow.

U.S. Pat. No. 3,034,882 discloses chemical fertilizer impregnated woodchips which when mixed with the soil conditions the soil by increasingits friability and liberates the fertilizer over an extended interval.

European Patent Application No. EP1074532A2 discloses a compostingadditive in the form of shredded lignocellulose materials coated withfungal enzymes which decompose plant materials in compost heaps.

U.S. Pat. No. 6,682,752 discloses soaking wood chips in castor oil toprovide a composition for mole control.

U.S. Patent Application No. 2004/0033248 discloses pesticidecompositions produced by absorbing or applying insecticides, herbicides,and/or fungicides to sawdust, wood chips, and ground corn cobs.

U.S. Patent Application No. 2006/0135365 discloses wood chipsinfiltrated with fertilizers, agricultural pesticides, and/or plantgrowth regulators.

It is also well known in the art that various time-release coatings canbe applied to such manufactured bioactive biomass compositions.

SUMMARY OF THE INVENTION

Herein we describe a new class of plant biomass feedstock particlescharacterized by consistent piece size and shape uniformity, highskeletal surface area, and good flow properties. This constellation ofcharacteristics makes the feedstock particles particularly advantageouscarriers for bioactive agents.

The subject particles of a plant biomass material having fibers alignedin a grain are characterized by a length dimension (L) alignedsubstantially parallel to the grain and defining a substantially uniformdistance along the grain, a width dimension (W) normal to L and alignedcross grain, and a height dimension (H) normal to W and L. Inparticular, the L×H dimensions define a pair of substantially parallelside surfaces characterized by substantially intact longitudinallyarrayed fibers, the W×H dimensions define a pair of substantiallyparallel end surfaces characterized by crosscut fibers and end checkingbetween fibers, and the L×W dimensions define a pair of substantiallyparallel top and bottom surfaces. The L×W surfaces of particles with L/Hdimension ratios of 4:1 or less are further elaborated by surfacechecking between longitudinally arrayed fibers. The length dimension Lis preferably aligned within 30° parallel to the grain, and morepreferably within 10° parallel to the grain. The plant biomass materialis preferably selected from among wood, agricultural crop residues,plantation grasses, hemp, bagasse, and bamboo.

As disclosed in the Examples, the particles are coated with bioactiveagents using well established techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of one-gram samples of the plant biomassmaterials used in the experiments described in the Examples: A, 2 mm×2mm hybrid Poplar particles; B, 4 mm×4 mm hybrid Poplar particles; C, abimodal mixture of the 2 mm and 4 mm hybrid Poplar particles; D, 4 mm×4mm Douglas fir particles; E, hand-sawn Douglas fir cubes; F, 4 mmcross-sheared corn stover particles;

FIG. 2 is a perspective view of the prototype rotary bypass shearmachine that was used to produce the plant biomass feedstock particlesshown in FIGS. 1A, B, C, D, and F; and

FIG. 3 is a graph of ion conductivity leachate data fromfertilizer-coated wood particles described in the Examples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

We have applied engineering design principles to develop a new class ofplant biomass feedstock particles with unusually large surface area tovolume ratios that can be manufactured in remarkably uniform sizes usinglow-energy comminution techniques. The particles exhibit a disruptedgrain structure with prominent end and some surface checks that greatlyenhance their skeletal surface area as compared to their envelopesurface area. Representative biomass feedstock particles are shown inFIGS. 1A, B, C, D, and F, which indicate how the nominalparallelepiped-shaped particles are cracked open by pronounced checkingthat greatly increases surface area.

The term “plant biomass” as used herein refers generally to encompassall plant materials harvested or collected for use as industrial andbioenergy feedstocks, including woody biomass, hardwoods and softwoods,energy crops like switchgrass, miscanthus, and giant reed grass, hemp,bagasse, bamboo, and agricultural crop residues, particularly cornstover.

The term “grain” as used herein refers generally to the arrangement andlongitudinally arrayed direction of fibers within plant biomassmaterials. “Grain direction” is the orientation of the long axis of thedominant fibers in a piece of plant biomass material.

The terms “checks” or “checking” as used herein refer to lengthwiseseparation and opening between plant fibers in a biomass feedstockparticle. “Surface checking” may occur on the lengthwise surfaces aparticle (particularly on the L×W surfaces); and “end checking” occurson the cross-grain ends (W×H) of a particle.

The term “extent” as used herein refers to an outermost edge on aparticle's surface taken along any one of the herein described L, W, andH dimensions (that is, either parallel or normal to the grain direction,as appropriate); and “extent dimension” refers to the longest straightline spanning points normal to the two extent edges along thatdimension. “Extent volume” refers to a parallelepiped figure thatencompasses a particle's three extent dimensions.

The term “skeletal surface area” as used herein refers to the totalsurface area of a biomass feedstock particle, including the surface areawithin open pores formed by checking between plant fibers. In contrast,“envelope surface area” refers to the surface area of a virtual envelopeencompassing the outer dimensions the particle, which for discussionpurposes can be roughly approximated to encompass the particle's extentvolume.

The terms “temperature calibrated conductivity,” “calibratedconductivity,” and “CC” as used herein refer to a measurement of theconductive material in an aqueous solution adjusted to a calculatedvalue that would have been read if the aqueous sample had been at 25° C.

The new class of plant biomass feedstock particles described herein canbe readily optimized in size, shape, and surface area to volume ratio toserve as carriers for bioactive agents. Representative carrier particlesare shown in FIG. 1 and described in the Examples.

Each particle is intended to have a specified and substantially uniformlength (L) along the grain direction, a width (W) tangential to thegrowth rings (in wood) and/or normal to the grain direction, and aheight (H) (termed thickness in the case of veneer) radial to the growthrings and/or normal to the W and L dimensions.

We have found it very convenient to use wood veneer from the rotarylathe process as a raw material. Peeled veneer from a rotary lathenaturally has a thickness that is oriented with the growth rings and canbe controlled by lathe adjustments. Moreover, within the typical rangeof veneer thicknesses, the veneer contains very few growth rings, all ofwhich are parallel to or at very shallow angle to the top and bottomsurfaces of the sheet. In our application, we specify the veneerthickness to match the desired wood particle height (H) tospecifications for particular end-use applications.

The veneer may be processed into particles directly from a veneer lathe,or from stacks of veneer sheets produced by a veneer lathe. Plantbiomass materials too small in diameter or otherwise not suitable forthe rotary veneer process can be sliced to pre-selected thickness byconventional processes. Our preferred manufacturing method is to feedthe veneer sheet or sliced materials into a rotary bypass shear with thegrain direction oriented across and preferably at a right angle to thefeed direction through the machine's processing head, that is, parallelto the shearing faces.

The rotary bypass shear that we designed for manufacture of woodfeedstock particles is a shown in FIG. 2. This prototype machine 10 ismuch like a paper shredder and includes parallel shafts 12, 14, each ofwhich contains a plurality of cutting disks 16, 18. The disks 16, 18 oneach shaft 12, 14 are separated by smaller diameter spacers (not shown)that are the same width or greater by 0.1 mm thick than the cuttingdisks 16, 18. The cutting disks 16, 18 may be smooth 18, knurled (notshown), and/or toothed 16 to improve the feeding of veneer sheets 20through the processing head 22. Each upper cutting disk 16 in our rotarybypass shear 10 contains five equally spaced teeth 24 that extend 6 mmabove the cutting surface 26. The spacing of the two parallel shafts 12,14 is slightly less than the diameter of the cutting disks 16, 18 tocreate a shearing interface. In our machine 10, the cutting disks 16, 18are approximately 105 mm diameter and the shearing overlap isapproximately 3 mm.

This rotary bypass shear machine 10 used for demonstration of themanufacturing process operates at an infeed speed of one meter persecond (200 feet per minute). The feed rate has been demonstrated toproduce similar particles at infeed speeds up to 2.5 meters per second(500 feet per minute).

The width of the cutting disks 16, 18 establishes the length (L) of theparticles produced since the veneer 20 is sheared at each edge 28 of thecutters 16, 18 and the veneer 20 is oriented with the fiber graindirection parallel to the cutter shafts 12, 14 and shearing faces of thecutter disks 16, 18. Thus, wood particles from our process are of muchmore uniform length than are particles from shredders, hammer mills andgrinders which have a broad range of random lengths. The desired andpredetermined length of particles is set into the rotary bypass shearmachine 10 by either installing cutters 16, 18 having widths equal tothe desired output particle length or by stacking assorted thinnercutting disks 16, 18 to the appropriate cumulative cutter width.

Fixed clearing plates 30 ride on the rotating spacer disks to ensurethat any particles that are trapped between the cutting disks 16, 18 aredislodged and ejected from the processing head 20.

We have found that the wood particles leaving the rotary bypass shearmachine 10 are broken (or crumbled) into short widths (W) due to inducedinternal tensile stress failures. Thus the resulting particles are ofgenerally uniform length (L) along the wood grain, as determined by theselected width of the cutters 16, 18, and of a uniform thickness (H,when made from veneer), but vary somewhat in width (W) principallyassociated with the microstructure and natural growth properties of theraw material species. Most importantly, frictional and Poisson forcesthat develop as the biomass material 20 is sheared across the grain atthe cutter edges 28 tend to create end checking that greatly increasesthe skeletal surface areas of the particles. Substantial surfacechecking between longitudinally arrayed fibers further elaborates theL×W surfaces when the length to height ratio (L/H) is 4:1 or less, andparticularly 2:1 or less.

The output of the rotary bypass shear 10 may be used as is for someend-uses such as soil amendment and industrial fiber production.However, many end-uses will benefit if the particles are screened intomore narrow size fractions that are optimal for end-use applicationsrequiring improved flowability and decay uniformity. In that case, anappropriate stack of vibratory screens or a tubular trommel screen withprogressive openings can be used to remove particles larger or smallerthan desired. In the event that the feedstock particles are to be storedfor an extended period or are to be fed into a conversion process thatrequires very dry feedstock, the particles may be dried prior tostorage, packing or delivery to an end user.

We have used this prototype machine 10 to make feedstock particles invarious lengths from a variety of plant biomass materials, including:peeled softwood and hardwood veneers; sawed softwood and hardwoodveneers; softwood and hardwood branches and limbs crushed to apredetermined uniform height or maximum diameter; cross-grain orientedwood chips and hog fuel; corn stover; switchgrass; and bamboo. The L×Wsurfaces of peeled veneer particles generally retain the tight-side andloose-side characteristics of the raw material. Crushed wood and fibrousbiomass mats are also suitable starting materials, provided that allsuch biomass materials are aligned across the cutters 16, 18, that is,with the shearing faces substantially parallel to the grain direction,and preferably within 10° and at least within 30° parallel to the graindirection.

We currently consider the following size ranges as particularly usefulbiomass feedstocks: H should not exceed a maximum from 1 to 16 mm, inwhich case W is between 1 mm and 1.5× the maximum H, and L is between0.5 and 20× the maximum H; or, preferably, L is between 4 and 70 mm, andeach of W and H is equal to or less than L. Surprisingly significantpercentages of the above preferably sized wood particles readily sink inwater, and this presents an opportunity to selectively sortlignin-enriched particles (by gravity and/or density) and moreeconomical preprocessing.

For flowability and high surface area to volume ratios, the L, W, and Hdimensions are selected so that at least 80% of the particles passthrough a ¼ inch screen having a 6.3 mm nominal sieve opening but areretained by a No. 10 screen having a 2 mm nominal sieve opening. Foruniformity as reaction substrates, at least 90% of the particles shouldpreferably pass through: a ¼″ screen having a 6.3 mm nominal sieveopening but are retained by a No. 4 screen having a 4.75 mm nominalsieve opening; or a No. 4 screen having a 4.75 mm nominal sieve openingbut are retained by a No. 8 screen having a 2.36 mm nominal sieveopening; or a No. 8 screen having a 2.36 mm nominal sieve opening butare retained by a No. 10 screen having a 2 mm nominal sieve opening.

Most preferably, the subject biomass feedstock particles arecharacterized by size such that at least 90% of the particles passthrough: a ¼ inch screen having a 6.3 mm nominal sieve opening but areretained by a ⅛-inch screen having a 3.18 mm nominal sieve opening; or aNo. 4 screen having a 4.75 mm nominal sieve opening screen but areretained by a No. 8 screen having a 2.36 mm nominal sieve opening; or a⅛-inch screen having a 3.18 mm nominal sieve opening but are retained bya No. 16 screen having a 1.18 mm nominal sieve opening; or a No. 10screen having a 2.0 mm nominal sieve opening but are retained by a No.35 screen having a 0.5 mm nominal sieve opening; or a No. 10 screenhaving a 2.0 mm nominal sieve opening but are retained by a No. 20screen having a 0.85 mm nominal sieve opening; or a No. 20 screen havinga 0.85 mm nominal sieve opening but are retained by a No. 35 screenhaving a 0.5 mm nominal sieve opening.

Suitable testing screens and screening assemblies for characterizing thesubject biomass particles in such size ranges are available from thewell-known Gilson Company, Inc., Lewis Center, Ohio, US(www.globalgilson.com). In a representative protocol, approximately 400g of the subject particles (specifically, the output of machine 10 with3/6″-wide cutters and ⅙″ conifer veneer) were poured into stacked ½″,⅜″, ¼″, No. 4, No. 8, No. 10, and Pan screens; and the stacked screenassembly was roto-tapped for 5 minutes on a Gilson® Sieve Screen ModelNo. SS-12R. The particles retained on each screen were then weighed.Table 1 summarizes the resulting data.

TABLE 1 Screen size ½″ ⅜″ ¼″ No. 4 No. 8 No. 10 Pan % retained 0 0.3 1.946.2 40.7 3.5 7.4These data show a much narrower size distribution profile than istypically produced by traditional high-energy comminution machinery.

Thus, the invention provides plant biomass particles characterized byconsistent piece size as well as shape uniformity, obtainable bycross-grain shearing a plant biomass material of selected thickness by aselected distance in the grain direction. Our rotary bypass shearprocess greatly increases the skeletal surface areas of the particles aswell, by inducing frictional and Poisson forces that tend to create endchecking as the biomass material is sheared across the grain. Theresulting cross-grain sheared plant biomass particles are useful ascarriers for bioactive agents, as described below.

EXAMPLES

Buckmaster recently evaluated electrolytic ion leakage as a method toassess activity access for subsequent biological or chemical processingof forage or biomass. (Buckmaster, D. R., Assessing activity access offorage or biomass, Transactions of the ASABE 51(6):1879-1884, 2008.) Heconcluded that ion conductivity of biomass leachate in aqueous solutionwas directly correlated with activity access to plant nutrients withinthe biomass materials.

In the following experiments, we compared ion leachate rates fromvarious fertilizer-coated biomass particles.

Materials

Wood particles of the present invention were manufactured in the abovedescribed machine 10, using either 3/16″ or 1/16″ wide cutters, fromgreen veneer of thicknesses corresponding to the cutter widths. Bothhybrid Poplar and Douglas fir particles were produced in this manner.Corn stover (no cobs) was cut into 100 mm billets, dehydrated, andsheared cross-grain through 3/16″ cutters.

The resulting particles were size screened. Approximately 400 g ofparticles were poured into stacked ⅜″, No. 4, ⅛″, No. 10, No. 16, No.35, No. 50, No. 100, and Pan screens; and the stacked screen assemblywas roto-tapped for 10 minutes on a Gilson® Sieve Screen Model No.SS-12R. Nominal 4 mm particles produced with the 3/16″ cutters werecollected from the pass ⅜″, no pass No. 4 screen. Nominal 2 mm particlesproduced with the 1/16″ cutters were collected from the pass ⅛″, no passNo. 16 screen.

Wood “cubes” were cut with a hand saw from ⅙″ Douglas fir veneer. Theveneer was sawn cross-grain into approximately 3/16″ strips. Then eachstrip was gently flexed by finger pressure to break off roughlyparallelogram-shaped pieces of random widths. The resulting pieces werescreened to collect cubes from the pass ⅜″, no pass No. 4 screen. As arepresentative sample, the extent length and width dimensions of 15cubes were measured with a digital caliper: the L dimensions had a meanof 7.5 mm, with a standard deviation of 1.8; and the W dimensions had amean of 4.6 mm with a SD of 1.1.

The particle and cube samples were dehydrated to constant weight at 43°C., and subdivided into control and experimental subsamples. Controlsubsamples were stored in airtight plastic bags until ion conductivityanalysis. The experimental subsamples were coated with liquid fertilizerusing the following protocol. 50 grams of the wood particles or cubeswere soaked and stirred for one hour in 800 ml of a 10× fertilizersolution prepared by dissolving 57.5 g of Miracle-Gro® Water Soluble AllPurpose Plant Food 24-8-16 (Scott's, Marysville, Ohio) in 0.5 gal dH₂O.20 g of the corn stover particles were submerged and soaked in 320 ml ofthe 10× fertilizer solution for one hour. The fertilizer coated carrierswere then drained onto a paper coffee filter and dehydrated overnight toconstant weight at 43° C.

Ion conductivity was measured as follows.

Equipment

Jenco® Model 3173/3173R Conductivity/Salinity/TDS/Temperature Meter

Corning® Model PC-420 Laboratory Stirrer/Hot Plate

Aculab® Model VI-1200 Balance

Methods

Ion conductivity of leachate in aqueous solution was assessed for eachsubsample by the following protocol:

(1) Measure the initial temperature compensated conductivity (CC, inmicroSiemens (μS)) of 500 ml of distilled water maintained at ˜25° C. ina glass vessel.

(2) Add a 10 g subsample of wood particles or cubes (or 5 g of cornstover particles) into the water, and stir at 250 RPM at ˜25° C. for 45minutes.

(3) Note and record the CC of the water at 15-minute intervals.

(4) Calculate an experimental CC value for comparison purposes bysubtracting the initial CC from the CC at 30 minutes.

Results

The observed CC data is shown in Table 2; and the hybrid Poplar data inrows 1 through 8 of Table 2 are plotted in FIG. 3.

TABLE 2 Soak & Swirl Time (minutes) # Biomass Particles 0 15 30 45 1 2mm hybrid Poplar control 1 3.0 63.2 65.2 66.5 Temperature 2 2 mm hybridPoplar control 2 3.1 55.8 57.1 60.9 Compensated 3 2 mm hybrid Poplar Exp(10x) 1 1.8 561 556 559 Conductivity (μS) 4 2 mm hybrid Poplar Exp (10x)2 2.4 555 548 506 5 4 mm hybrid Poplar control 1 2.4 47.5 55.3 59.3 6 4mm hybrid Poplar control 2 2.3 50.3 57.8 61.6 7 4 mm hybrid Poplar Exp(10x) 1 2.3 317 329 458 8 4 mm hybrid Poplar Exp (10x) 2 2.4 394 438 4589 Biomodal hybrid poplar Exp (10x) 2.3 498 534 547 10 4 mm Douglas fircontrol particles 2.3 85.5 94.1 95.8 11 4 mm Douglas fir Exp (10x)particles 1.9 271 335 363 12 Douglas fir cubes, control 2.2 55.4 80.395.9 13 Douglas fir cubes, Exp (10x) 2.6 126.9 160.3 182.9 14 4 mm cornstover control 1.7 638 759 809 15 4 mm corn stover Exp (10x) 2.2 11031252 1326

Referring to the hybrid Poplar CC data shown in rows 1 to 8 and FIG. 3,several trends are apparent. First, the fertilizer coated experimentalparticles released roughly 10 times more ions than the uncoated controlparticles. Second, 10 g of the 2 mm experimental particles released moreions than 10 g of the 4 mm experimental particles. Third, the replicate2 mm experimental particles exhibited roughly similar CC profiles, asdid the 4 mm experimental particles. From these observations we surmisethat the consistent size and shape uniformity and high surface area ofthe subject particles foster a high and consistent coating (presumablydue to diffusion-driven absorption and/or adsorption processes) ofinorganic fertilizer ions to the biomass matrix, as well as toempirically determinable release rates (presumably by diffusion) afterdrying and exposure to moisture.

Row 9 shows CC data from a bimodal hybrid Poplar sample, in this casecomposed of 5 g of the 2 mm experimental 10× particles admixed with 5grams of the 4 mm 10× experimental particles. As used herein the term“monomodal” refers to a feedstock that contains substantially one sizeof particle, whereas a “bimodal” feedstock contains two sizes ofparticles as characterized by exhibiting a continuous probabilitydistribution having two different modes (that is, two relativelydistinct peaks identifiable by size screening). “Multimodal” indicatesexhibiting a plurality of such sizes or peaks. This particular mixturehad two equal size peaks, at 2 mm and 4 mm, and the resulting CC data(row 10) falls somewhat in between the CC data of its monomodalconstituents (rows 3-4 and 7-8).

Rows 10 and 11 show CC data from uncoated and coated 4 mm particles ofDouglas fir, a slow growing softwood having a somewhat higher densitythan fast-growing hybrid Poplar hardwood. The CC profiles of the 4 mmsoftwood (rows 10 and 11) and the hybrid hardwood particles (rows 7 and8) are somewhat different, which indicates that different types of woodwill exhibit different capacities to absorb/adsorb and/orrelease/diffuse inorganic fertilizer ions.

Rows 12 and 13 show that uncoated and coated cubes exhibit a muchtighter CC uptake/release profile than wood particles (rows 10 and 11).Despite having a larger envelope volume, the cubes had an experimentalCC value of 61 v. 241 for the particles. These data are consistent withthe elaborated skeletal surface area of the subject particles, which arecharacterized by pronounced end checking and some surface checking.

-   -   Rows 14 and 15 show CC data from uncoated and coated 4 mm corn        stover particles. These particle samples were anatomically        heterogeneous and contained substantially equal amounts by        weight of cross-grain stalk (rind with pith attached) and leaf        particles, along with about 5% tassel particles and inorganic        grit. This corn stover CC data was relatively high, even though        generated using half the sample size as in the wood experiments        (5 g v. 10 g). Visual observation indicated that the        fertilizer's blue-green color localized in the pith, which        suggests that the pith adsorbed/released an abundant amount of        the fertilizer ions. The grit component undoubtedly boosted the        observed CC levels as well.

We observe generally from the Table 2 data that soluble fertilizeruptake and release as measured by CC is a useful comparative indicatorof the skeletal surface areas of biomass particles. These datafurthermore indicate that particle size, shape, and surface area tovolume ratio affect the uptake and release of chemical ions. We concludethat such particle characteristics can be empirically modified andoptimized for particular carrier purposes as, for example, described inthe prior U.S. patent publications cited herein, all of which are herebyincorporated by reference in their entireties. We envision that the 2mm×2 mm particle size is particularly suitable carrier for time releaseencapsulation following uptake of one or more bioactive agents, toprovide a flowable product with high bulk density and uniform releaserate.

While the preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. Particles of a plantbiomass material coated with a bioactive agent, the particles beingcharacterized by a length dimension (L) aligned substantially parallelto a grain direction and defining a substantially uniform distance alongthe grain, a width dimension (W) normal to L and aligned cross grain,and a height dimension (H) normal to W and L, wherein the L×H dimensionsdefine a pair of substantially parallel side surfaces characterized bysubstantially intact longitudinally arrayed fibers, the W×H dimensionsdefine a pair of substantially parallel end surfaces characterized bycrosscut fibers and end checking between fibers, and the L×W dimensionsdefine a pair of substantially parallel top and bottom surfaces.
 2. Theparticles of claim 1, wherein L is aligned within 10° parallel to thegrain direction.
 3. The particles of claim 1, wherein L is alignedwithin 30° parallel to the grain direction.
 4. The particles of claim 1,wherein L/H is 4:1 or less and wherein the top and bottom surfaces arecharacterized by surface checking between longitudinally arrayed fibers.5. The particles of claim 1, wherein H does not exceed a maximum from 1to 16 mm, W is between 1 mm and 1.5× the maximum H, and L is between 0.5and 20× the maximum H.
 6. The particles of claim 1, wherein L is between4 and 70 mm, and each of W and H is equal to or less than L.
 7. Theparticles of claim 1, characterized by size such that at least 80% ofthe particles pass through a ¼ inch screen having a 6.3 mm nominal sieveopening but are retained by a No. 10 screen having a 2 mm nominal sieveopening.
 8. The particles of claim 1, characterized by size such that atleast 90% of the particles pass through either: an ¼ inch screen havinga 6.3 mm nominal sieve opening but are retained by a ⅛-inch screenhaving a 3.18 mm nominal sieve opening; a No. 4 screen having a 4.75 mmnominal sieve opening screen but are retained by a No. 8 screen having a3.18 mm nominal sieve opening; a ⅛-inch screen having a 3.18 mm nominalsieve opening but are retained by a No. 16 screen having a 1.18 mmnominal sieve opening; a No. 10 screen having a 2.0 mm nominal sieveopening but are retained by a No. 35 screen having a 0.5 mm nominalsieve opening; a No. 10 screen having a 2.0 mm nominal sieve opening butare retained by a No. 20 screen having a 0.85 mm nominal sieve opening;or, a No. 20 screen having a 0.85 mm nominal sieve opening but areretained by a No. 35 screen having a 0.5 mm nominal sieve opening. 9.The particles of claim 1, wherein the plant biomass is selected fromamong wood, agricultural crop residues, plantation grasses, hemp,bagasse, and bamboo.
 10. The particles of claim 9, wherein the wood is aveneer.
 11. The particles of claim 1, characterized by having a bimodalor multimodal size distribution.